Electrostatic dissipating fabric and garments formed therefrom

ABSTRACT

Electrostatic dissipating fabrics incorporating spun yarns which include conductive staple fiber constituents incorporated within the spun yarns. The fabrics may be of either a woven or knit construction. The conductive fiber constituents are dispersed at an effective concentration to establish a network of charge carrying junctions within and between the individual yarns. The large number of junctions between the yarns facilitates the dissipation of static electricity between regions of a garment formed by the yarns. In particular, the fabric retains a high degree of conductivity across seams within the garment even after multiple washings.

TECHNICAL FIELD

[0001] The present invention relates generally to electrostaticdissipating fabrics and more particularly to electrostatic dissipatingfabrics incorporating spun yarns which include conductive staple fiberconstituents incorporated within the spun yarns.

BACKGROUND

[0002] It is well known that when clothing fabric is used inenvironments such as a clean room or other areas where humidity isreduced or controlled, such fabrics may be susceptible to anaccumulation of static electricity. This accumulation in staticelectricity may be particularly pronounced as humidity is reduced due tothe fact that the static electricity cannot dissipate into the air. Aswill be well recognized, under extreme circumstances an accumulation instatic electricity may give rise to a rapid electric discharge in theform of an arc when the fabric is brought into contact with a groundedstructure.

[0003] In recent years so-called “solid state” electronic circuitryusing integrated circuits on semi-conductor materials such as silicon,and the like has moved towards ever finer circuit arrangements. Whilesuch technology and the resulting electronic components are extremelyuseful in carrying out a range of functions with very small spacerequirements, the decreased circuit geometries within those structureshas made the electronic components highly susceptible to damage fromexternal electric charges. In order to avoid the potential for damagewhich may result from the rapid discharge of static electricity, it isdesirable to avoid the accumulation of static electricity withingarments and other textile structures used within an electronicsmanufacturing environment.

[0004] In order to facilitate the dissipation of static electricity awayfrom a garment and into the atmosphere, it is desirable to distributeany electric charge substantially across the garment thereby providingthe highest possible surface area for atmospheric dissipation. Thesubstantial conduction of electric charge throughout the garment alsopermits the effective use of grounding wires in the form ofbracelet-like structures attached to grounded cords which may be worn bythe user of the garment.

[0005] Garments such a lab coats and the like which may be worn duringthe assembly of electronic components are normally formed by the seamedattachment of fabric panels. If the electrical resistance betweensegments of the garment is too high, the possibility may exist forsegments of the garment to become conductively isolated. If theseconductively isolated segments of the garment cannot dissipate the builtup static electricity and/or are not directly connected to a groundingsource, potentially undesirable and uncontrolled rapid discharge ofstatic electricity may occur on a periodic basis. As indicated above,the magnitude of such a discharge need not be substantial in order to bepotentially damaging to sophisticated electronic circuitry.

[0006] In order to address these issues, a number of fabricconstructions and materials have been previously proposed. By way ofexample only, various arrangements are proposed in the following U.S.patents each of which is incorporated herein by reference in itsentirety. In U.S. Pat. No. 2,845,962 an anti-static fabric is disclosedwhich is made from a fibrous material containing electrically conductivecarbon black. U.S. Pat. No. 3,288,175 teaches the incorporation of asmall quantity of metallic fibers within the textile fiber materials toproduce an anti-static fabric. U.S. Pat. No. 3,586,597 discloses the useof a fiber which is coated with a resinous matrix of finely dividedsilver or carbon black. U.S. Pat. No. 4,255,487 discloses anelectrically conductive textile fiber in which electrically conductiveparticles are suffused into a filamentary polymer substrate in anannular region located at the periphery of the filamentary polymersubstrate. U.S. Pat. No. 4,869,951 discloses a static dissipatingtextile incorporating non-linear carbonaceous fibers or filaments.Currently, fabric dissipating fabric for use in clothing articles inelectronic manufacturing environments generally uses an arrangement ofsubstantially non-conductive yarns in combination with conductivefilament yarns. By way of example only, and not limitation, variousconstructions incorporating such conductive filament yarns are describedin U.S. Pat. Nos. 4,557,968 and 4,606,968.

[0007] In the past, it has been found that garments such as lab coatsand the like formed from prior electrostatic dissipating fabrics havebeen susceptible to an overall reduction in conductivity followingmultiple uses and washings. In particular, it has been found that thesleeve to sleeve conductivity measured between the cuff portions ofsleeves on such garments may dramatically degrade due to the naturallyoccurring seam combing or separation which occurs between the panels offabric forming the garment at the shoulder seams connecting the sleevesto the body of the garment. That is, after multiple washings the seamsbetween the sleeves and the body portion of the garment may tend toundergo a very slight separation. Due to the relatively dispersed natureof the conductive filament yarns in the fabric forming the panels ofmaterial, this separation may give rise to a substantial reduction inconductivity across the seam. Thus, electrostatic charges may beprevented from efficiently traveling across the seam junction betweenthe sleeves and the body portion of the garment. This reduction inconductivity may give rise to the potentially undesirable buildup ofstatic electricity within portions of the garment.

SUMMARY

[0008] The present invention provides advantages and alternatives overthe prior art by providing electrostatic dissipating fabricsincorporating spun yarns which include conductive staple fiberconstituents incorporated within the spun yarns. The fabrics may be ofeither a woven or knit construction and are particularly adapted for usein garments worn during the construction of electronic components wherearcing from accumulated static electricity is to be avoided. Theconductive fiber constituents are dispersed at an effectiveconcentration to establish a network of charge carrying junctions withinand between the individual yarns. The large number of junctions betweenthe yarns facilitates the dissipation of static electricity betweenregions of a garment formed by the yarns. In particular, the fabricretains a high degree of conductivity across seams within the garmenteven after multiple washings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The present invention will now be described by way of exampleonly, with reference to the accompanying drawings which constitute apart of the specification herein and in which:

[0010]FIG. 1 is a schematic illustration of a lab coat as may be worn inan electronics manufacturing environment;

[0011]FIG. 2 is an exemplary woven fabric construction incorporating agrid arrangement of conductive filament yarns in combination with spunyarns;

[0012]FIG. 3 illustrates a section of spun yarn incorporatingfilamentary staple elements of electrically conductive character;

[0013]FIG. 4 is a plan view of the interface between two panels of wovenfabric formed using the yarn of FIG. 3; and

[0014]FIG. 5 is a plan view of an exemplary knit fabric construction asmay be formed using the yarn of FIG. 3.

[0015] While the invention has been illustrated and generally describedabove and will hereinafter be described in connection with certainpotentially preferred embodiments, procedures and practices, it is to beunderstood that in no event is the invention to be limited to suchillustrated and described embodiments, procedures and practices. On thecontrary, it is intended that the present invention shall extend to allalternatives and modifications as may embrace the principles of thisinvention within the true spirit and scope thereof.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0016] Reference will now be made to the drawings wherein, to the extentpossible, like elements are designated by like reference numeralsthroughout the various views. Turning to the drawings, in FIG. 1, ajacket or lab coat 10 as may be utilized in an electronics manufacturingenvironment is illustrated. As shown, the lab coat 10 includes a mainbody portion 12 adapted to cover the torso of a user and two sleeveportions 14 extending away from the body portion 12 to provide coverageacross the arms of a user. As illustrated, the sleeves 14 are adjoinedto the body portion 12 along seams 16 such as sewn seams or the like. Aswill be appreciated, additional seams may be disposed in adjoiningrelation between the front of the lab coat 10 and the rear of the labcoat 10 in a manner as will be well know to those of skill in the art.

[0017] Regardless of the actual construction of the lab coat 10, theindividual portions thereof are preferably formed from panels of wovenor knitted fabric which are sewn into a desired configuration. Thus, atthe seams 16 as well as at other seams within the garment 10 discretepanels of fabric are joined together in slightly overlapping relation toone another. In a sewn seam construction, this adjoined relation isestablished and maintained by passing a stitching yarn 18 repetitivelyacross the interface between the two panels of fabric at the interfaceof such panels of fabric.

[0018] In accordance with the present invention, the construction of thepanels of fabric forming the segments of the garment 10 is preferablysuch that a controlled degree of electrical conductivity is establishedand maintained throughout the garment 10. One exemplary prior art fabricconstruction for use in the formation of the garment 10 is illustratedschematically in FIG. 2. As shown, in this prior art construction, amultiplicity of conductive filaments of material such as graphite or thelike are interwoven in a substantially disperse grid-like arrangementwith a multiplicity of multi-filament spun yarns 22. As will beappreciated, in the illustrated prior art construction, the conductivecircuit through the fabric is established by the junctions formed at thecrossing points 24 between the conductive filament yarns 20. As shown,such crossing points 24 are dispersed relatively infrequently throughoutthe fabric construction. Moreover, in the event that two panels of suchmaterial are seamed together, the electrical connection between the twoseamed panels is dependent upon the bridging contact between theconductive filament yarns 20 in each of the panels. Since suchconductive filament yarns 20 are dispersed sparingly through the overallfabric, a disconnection of even a small number of the junctionsestablished across the seam such as during washing or use willnegatively impact the ability to efficiently conduct electricity acrossa seam structure. While this deficiency may be addressed by increasingthe number of conductive filament yarns 20, such an increase may reducethe comfort of the fabric while substantially increasing manufacturingcosts.

[0019] In order to promote the efficient distribution of electriccharges throughout the garment 10, the present invention utilizes afabric formed from a conductive spun yarn 40 which is formed into aconductive fabric 50. The fabric may be of either a woven construction(FIG. 4) or may be of a knit construction (FIG. 5).

[0020] As illustrated, the conductive spun yarn 40 incorporates discreteconductive staple fibers 52 which are spun into the yarn in combinationwith staple fibers of substantially nonconductive polymeric or naturalmaterial such as (but not limited to) polyester, nylon, cotton, andmixtures thereof. As will be appreciated by those of skill in the art,by the term “staple fiber” is meant any discrete length fiber which maybe formed by known spinning techniques such as ring spinning, open endspinning or air jet spinning into a coordinated yarn structure. By wayof example only, and not limitation, it is contemplated that theconductive staple fibers 52 are preferably formed from a substantiallyelectrically conductive carbonaceous material such as graphite orgraphite suffused fibers of substantially linear geometry having staplelengths in the range of about 1 mm to about 150 mm. However, it iscontemplated that other staple fibers of electrically conductivecharacter may likewise be utilized including relatively short lengths ofnatural or synthetic fibers rendered conductive by the deposition of aconductive polymeric material such as polypyrole, polyaniline, or otherconductive polymers as described in U.S. Pat. No. 4,803,096 to Kuhn etal. the teachings of which are incorporated by reference. It is alsocontemplated that the conductive staple fibers 52 may be formed fromnatural or synthetic fibers rendered conductive by deposition of ametallic material such as silver or copper sulfide.

[0021] Regardless of the actual construction and composition of theconductive staple fibers 52, such conductive staple fibers 52 arepreferably dispersed throughout the conductive spun yarn 40 in a mannerso as to render the conductive spun yarn 40 suitable for transmitting anelectric charge therethrough and across seams formed between panels ofthe fabric. In this regard, the electrical conductivity of the garment10 may be measured by standardized electrostatic dissipation (ESD) testssuch as the ESD Association's Test Method STM 2.1-1997. In such a test,leads are clipped between the sleeves 14 and a 10 volt charge is appliedbetween the leads. The resistance between the leads is then measured.This test is carried out at a controlled relative humidity of 12%. Insuch a test, the measured sleeve to sleeve resistance is preferably lessthan 10¹² Ohms and is more preferably in the range of 10⁴ to about 10¹²Ohms. It is most preferably in the range of about 10⁴ to about 10⁸ Ohms.While such tests provide useful standards for evaluation of conductivityin an overall garment, the fabric making up such garments may also bethe subject of evaluation independent of the garment so as to discountthe effects of factors such as garment size, numbers of seams and thelike. One recognized test method for measuring electrical resistivity ina fabric is set forth at AATCC Test Method 76-1987 (incorporated byreference). According to this method, resistivity is reported in unitsof ohms per square based upon the following formula:$\frac{{Measured}\quad {Resistance}\quad ({ohms}) \times {Width}\quad {of}\quad {Specimen}}{{Distance}\quad {Between}\quad {Electrodes}}$

[0022] When measured according to this test procedure at 20% relativehumidity using a 2 inch×2 inch specimen at a 100 volt potential and 1inch electrode spacing, fabrics according to the present inventionpreferably have generally similar resistivity measurements in both themachine and cross-machine directions with such levels preferably beingless than about 1,000,000,000 ohms per square and more preferably in therange of about 100,000 to 100,000,000 ohms per square. In someenvironments, resistivity levels substantially below about 100,000 ohmsper square may be undesirable due to the garment becoming overlyconductive.

[0023] In order to achieve the desired electrical resistance levels, itis contemplated that the conductive fiber content in the spun yarn 40 ispreferably in the range of about 1% to about 5% by weight and will morepreferably be in the range of about 1% to about 3% by weight with theremainder of the conductive spun yarn 40 being made up of substantiallynon-conductive polymeric or natural fibers. By way of example, and notlimitation, one contemplated composition for the conductive yarn 40 is63% polyester fiber, 35% cotton fiber, and 2% carbon suffused acrylicstaple fibers. In one exemplary construction, such a yarn may be spuninto a 26/1 yarn for use in the warp direction of the conductive fabric50 and into a 16/1 construction for use in the filling direction of theconductive fabric 50.

[0024] As best illustrated in FIG. 4, the utilization of the conductivespun yarn 40 in the conductive fabric 50 establishes a substantiallyconductive arrangement with electrical junctions being established bothalong the length of each of the conductive yarns 40 as well as at anypoint of contact between the conductive yarns 40. That is, an electricalconnection is established at every crossing point between the warp yarnsand the fill yarns as well as at every contact point along a seam line54. Thus, unlike the prior art construction illustrated in FIG. 2,wherein electrical junctions are established only sporadicallythroughout the fabric structure, in the contemplated conductive fabric50, the number of connections is virtually unlimited thereby providingan improved conduction path for static electricity through theconductive fabric 50. Of course, it is to be understood that while thewoven version of the conductive fabric 50 is illustrated as being in aso-called “plain weave” construction, other weave constructions as wellas knit constructions (FIG. 5) and the like as will be well know tothose of skill in the art may be likewise be utilized if desired. Theinvention may be further understood by reference to the followingnon-limiting example.

EXAMPLE

[0025] A woven fabric was formed with a plain weave construction usingan open end spun warp yarn of 26/1 construction and a fill yarn of 16/1open end spun construction. Both the warp yarn and the fill yarncontained 63% polyester fiber, 35% cotton fiber, and 2% carbon fiber.The polyester fiber was KoSa T121 1.2 denier per filament fiber with astaple length of 1.5 inches. The cotton fiber had an estimated staplelength of {fraction (31/32)} of inch. The carbon fiber was a carbonsufused acrylic having a 1.5 inch staple length and a filament lineardensity of 3 denier. One such acrylic material is believed to beavailable from Sterling Fibers having a place of business in Pace Fla.,USA. The resultant yarns were thereafter woven on a standard rapierweaving machine in a construction of about 92 ends per inch by 48 picksper inch. A lab coat was thereafter constructed from panels of theresultant woven fabric with seams adjoined by traditional yarnstitching. The resulting garment was thereafter subjected to ESDAssociation Test Method STM 2.1-1997 at 10 volts and 12% relativehumidity. The measured electrical resistance after a controlled numberof washings is set forth at Table 1. TABLE 1 No. of Washings Sleeve toSleeve Resistance (Ohms) 0  8.3 × 10**5 10 3.65 × 10**5 25  4.9 × 10**550  7.5 × 10**5 75 1.05 × 10**6 100 1.57 × 10**6

[0026] Of course, it is contemplated that conductive filament materialsother than carbon suffused acrylic may likewise be utilized. Inparticular, it is contemplated that low percentages of nylon as well aspolyester and the like which have been rendered conductive may also beused. By way of example only, one such nylon fiber material is believedto be available from Shakespeare Fibers having a place of business inColumbia, S.C., USA. As previously indicated, electrical conductivity inany of the materials as may be used in the conductive staple fibers maybe imparted by carbonaceous materials as well as by the use ofelectrically conductive polymers or metallic additions.

[0027] While the present invention has been illustrated and described inrelation to certain potentially preferred embodiments, procedures, andpractices, it is fully contemplated that modifications and variations tothe present invention will no doubt occur to those of skill in the artupon reading the preceding description and/or through practice of theinvention. It is therefore intended that the invention shall extend toall such modifications and variations which incorporate the boardprinciples of the present invention within the full spirit and scopethereof.

What is claimed is:
 1. A static electricity dissipating fabriccomprising a plurality of spun yarns held together in crossing relationto one another in a coordinated woven or knit construction, wherein saidspun yarns comprise a plurality of electrically conductive staple fibersin spun relation with a plurality of substantially nonconductive naturalor synthetic staple fibers and wherein said plurality of electricallyconductive staple fibers are dispersed throughout said spun yarns suchthat said plurality of electrically conductive staple fibers define anetwork of electrically conductive junctions along the length of saidspun yarns and between said spun yarns at locations where said spunyarns meet.
 2. A static electricity dissipating fabric as recited inclaim 1, wherein said spun yarns are ring spun yarns.
 3. A staticelectricity dissipating fabric as recited in claim 1, wherein said spunyarns are open end spun yarns.
 4. A static electricity dissipatingfabric as recited in claim 1, wherein said spun yarns are air jet spunyarns.
 5. A static electricity dissipating fabric as recited in claim 1,wherein said substantially nonconductive natural or synthetic staplefibers are selected from the group consisting of polyester staple fiberfibers, cotton staple fibers and blends thereof.
 6. A static electricitydissipating fabric as recited in claim 1, wherein said plurality of spunyarns comprise about 65% to about 99% by weight polyester staple fibersand about 0% to about 34% by weight cotton fibers and about 1% to about5% by weight of electrically conductive carbonaceous staple fibers ofsubstantially linear geometry.
 7. A static electricity dissipatingfabric as recited in claim 6, wherein said static electricitydissipating fabric is of a woven construction and wherein said staticelectricity dissipating fabric is characterized by an electricalresistance in the range of about to about 100,000 to about 100,000,000ohms per square when measured according to AATCC Test Method 76-1987using a 100 volt potential and 1 inch electrode spacing at 20% relativehumidity.
 8. A static electricity dissipating fabric comprising aplurality of spun yarns held together in crossing woven relation to oneanother, wherein said spun yarns comprise a plurality of electricallyconductive carbonaceous staple fibers of substantially linear geometryin spun relation with a plurality of substantially nonconductive naturalor synthetic staple fibers and wherein said plurality of electricallyconductive carbonaceous staple fibers are dispersed throughout said spunyarns such that said plurality of electrically conductive carbonaceousstaple fibers define a network of electrically conductive junctionsalong the length of said spun yarns and between said spun yarns atlocations where portions of said spun yarns meet within the fabric.
 9. Astatic electricity dissipating fabric as recited in claim 8, whereinsaid spun yarns are ring spun yarns.
 10. A static electricitydissipating fabric as recited in claim 8, wherein said spun yarns areopen end spun yarns.
 11. A static electricity dissipating fabric asrecited in claim 8, wherein said spun yarns are air jet spun yarns. 12.A static electricity dissipating fabric as recited in claim 8, whereinsaid substantially nonconductive natural or synthetic staple fibers areselected from the group consisting of polyester staple fiber fibers,cotton staple fibers and blends thereof.
 13. A static electricitydissipating fabric as recited in claim 8, wherein said plurality of spunyarns comprise about 65% to about 99% by weight polyester staple fibersand about 0% to about 34% by weight cotton fibers and about 1% to about5% by weight of electrically conductive carbonaceous staple fibers ofsubstantially linear geometry.
 14. A static electricity dissipatingfabric as recited in claim 13, wherein said static electricitydissipating fabric is characterized by an electrical resistance in therange of about to about 100,000 to about 100,000,000 ohms per squarewhen measured according to AATCC Test Method 76-1987 using a 100 voltpotential and 1 inch electrode spacing at 20% relative humidity.
 15. Astatic electricity dissipating fabric as recited in claim 13, whereinthe electrically conductive carbonaceous staple fibers are carbonsuffused acrylic fibers.
 16. A static electricity dissipating fabric asrecited in claim 15, wherein the carbon suffused acrylic fibers arecharacterized by a staple length of about 0.5 to about 3.5 inches.
 17. Astatic electricity dissipating fabric of woven construction having awarp direction and a fill direction, said static electricity dissipatingfabric comprising a plurality of spun yarns disposed in both the warpdirection and the fill direction and wherein said spun yarns comprise aplurality of electrically conductive carbonaceous staple fibers ofsubstantially linear geometry in spun relation with a plurality ofsubstantially nonconductive natural or synthetic staple fibers andwherein said plurality of electrically conductive carbonaceous staplefibers are dispersed throughout said spun yarns such that said pluralityof electrically conductive carbonaceous staple fibers define a networkof electrically conductive junctions along the length of said spun yarnsand between said spun yarns at locations where portions of said spunyarns meet within the fabric, wherein said plurality of spun yarnscomprise about 65% to about 99% by weight polyester staple fibers andabout 0% to about 34% by weight cotton fibers and about 1% to about 5%by weight of electrically conductive carbonaceous staple fibers ofsubstantially linear geometry.
 18. A static electricity dissipatingfabric as recited in claim 17, wherein said static electricitydissipating fabric is characterized by an electrical resistance in therange of about to about 100,000 to about 100,000,000 ohms per squarewhen measured according to AATCC Test Method 76-1987 using a 100 voltpotential and 1 inch electrode spacing at 20% relative humidity.
 19. Astatic electricity dissipating fabric as recited in claim 17, whereinsaid spun yarns are ring spun yarns.
 20. A static electricitydissipating fabric as recited in claim 17, wherein said spun yarns areopen end spun yarns.
 21. A static electricity dissipating fabric asrecited in claim 17, wherein said spun yarns are air jet spun yarns. 22.A garment formed from seamed panels of the static electricitydissipating fabric as recited in claim
 17. 23. A garment as recited inclaim 22, wherein said garment is a lab coat and wherein said lab coatis characterized by a sleeve to sleeve electrical resistance of lessthan about 100,000,000 ohms after 100 washings when measured accordingto ESD Association Test Method STM 2.1-1997 at 10 volts and 12% relativehumidity.
 24. A garment as recited in claim 22, wherein said garment isa lab coat and wherein said lab coat is characterized by a sleeve tosleeve electrical resistance in the range of less than about 10,000,000ohms after 100 washings when measured according to ESD Association TestMethod STM 2.1-1997 at 10 volts and 12% relative humidity.
 25. A garmentas recited in claim 22, wherein said garment is a lab coat and whereinsaid lab coat is characterized by a sleeve to sleeve electricalresistance of less than about 5,000,000 ohms after 100 washings whenmeasured according to ESD Association Test Method STM 2.1-1997 at 10volts and 12% relative humidity.